<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>test div</title>
</head>
 
		<style>
 
 .box{
	display:flex;
}
.left,.right{
	width:400px;
	height: 900px;
	background-color: cadetblue;
}
.center{
	flex:1;
	background-color: darkgreen;
}
		</style>
 
 
<body>
	<div class="box">
		<div class="left">我是左边</div>
		<div class="center">我是中间</div>
		<div class="right">我是右边</div>
	</div>
</body>
</html>
